I use to use a lot of plastic resin, it is great as you can encase just about anything in it from photos to leaves, and you can dye it opaque or a solid colour, put glitter or metal with in it.
You can usually buy small amounts from most craft and art stores, however i use to buy it in larger quantity's from a boat supply shop in Brentford, Middlesex, they supply company's using to make pieces for film sets, here's the link:http://www.thefibreglassshop.co.uk/
It usually comes in a oil can type vessel with a smaller separate bottle containing a catalyst. Everything has to measured out accurately as the catalyst can cause it to over heat and start smoking! It needs to be used in a very well ventilated room or outside, you can also buy this strange rubber plastic that you can melt in a microwave pour it over an object peel it off and then use it as a mold for the resin.
A few tips:
nail polish remover wiped on the piece takes away the stickiness.
T-polish/T-Cut normally used to polish cars, polishes pieces really well, even the finest grades of wet and dry sand paper will leave marks.
Its great fun to use and it is best to use a ice cube tray first to do tests in.